Solid state video camera

Abstract: By applying the offset sampling using four-plane prism provided with four solid state imaging devices at four light output planes, chromatic aberration of lenses is eliminated even to the peripheral part of the imaging plane, and moire suppression effect is much enhanced. Furthermore, by using a plural number of matrix circuits, and by producing the luminance signal by changing the matrix ratios in low frequency range and in high frequency range, moire suppression effect is further enhanced, and luminance error is also eliminated.

Description: FIELD OF THE INVENTION AND RELATED ART STATEMENT 1. FIELD OF THE INVENTION The present invention relates to a video camera using solid-state imaging devices 2. DESCRIPTION OF THE RELATED ART The resolution of a video camera using a solid state picture imaging device is determined by a number of pixels of the solid state imaging device used therein. Improvement of the resolution of a solid state imaging device can be realized by increasing the number of pixels of the solid state imaging device. However, increasing of the pixel number while keeping the imaging size of the device constant results in a reduction of the size of individual pixels, and it introduces lowering in its important performance characteristics such as sensitivity and dynamic range. Therefore, the improvement of resolution of a solid state imaging device by adapting the increase of pixel number was feasible only in the extent that the sensitivity and the dynamic range obtainable from the device could fulfill the performance required for a video camera. Heretofore, in order to obtain a high resolution capability using a solid state imaging device having a limited number of pixels, the RGB offset sampling has widely been investigated. The detail is described in "3 CCD Camera Scheme" (Television Gakkai Gijutsu Hokoku (Technical Report of Japan Television Engineering Institute), ED-395, authors: Yamanaka, Yamazaki, Hashimoto, Abe, Ochi, published on 28, Sept., 1978). In the following, explanation is given on the configuration of the RGB offset sampling scheme and problems thereon. The basic configuration comprises a three primary color prism, three solid state imaging devices respectively for green channel, blue channel, and red channel. At the three primary color prism, setting-positions of the solid state imaging devices for the red channel and for the blue channel are taken to be offset by an amount of half pitch of the horizontal pixel pitch in the horizontal direction with respect to the setting-position of the solid state device for the green channel in reference to its optical image. As a result of the above-mentioned offset, for the luminance signal which is obtained by combining respective color channel signals, the number of sampling points upon an optical image becomes effectively increased, and thereby the moire is suppressed and hence a high resolution is gained. In the RGB offset sampling scheme, there are two problems. First one is that, in the peripheral part of an imaging plane of a solid state device, due to the chromatic aberration of lens, the above-mentioned moire suppression capability is no longer available. As one of the chromatic aberrations of lens, the lateral chromatic aberration is known such that the size of focused image is dependent on light wavelength. According to the conventional RGB offset sampling scheme, the pixel is offset among different color channels. Therefore, the moire suppression function is insufficient as the area considered comes closer to the periphery of the imaging plane owing to influence of the chromatic aberration of the lens. Secondly, since the solid state imaging devices for the red channel and the blue channel are placed at the same or equivalent position for an optical image, that is, at respective positions at which the same image is focused and offsetting is made only for the green channel, the moire suppression effect is limited only to green channel, but cannot be obtained for those colors not including green light, namely for such colors as red, blue, and magenta. US-A-4,725,880 discloses in column 2, lines 51-66, a known color solid state imaging apparatus in accordance with the preamble of present claim 1, wherein four imagers are used as in the present invention. EP-A-0 476 421 discloses a solid state video camera using a spatial pixel shift with a circuit for producing brightness signal having at least a first and a second matrix circuit wherein the first matrix ratio is predetermined by the television standard and the second matrix ratio is set to a different but fixed value so that a spurious component in the brightness signal is reduced. Similarly, WO-A-85/05526 discloses a method for enhancing the resolution of color television cameras. This method is also directed to a solid state video camera wherein a signal processing part has at least a first and a second matrix circuit wherein the matrix ratio of said second matrix circuit is likewise fixed and different from the television standard. Document SMPTE Journal, vol. 102, no. 3, March 1993, White Plains, NY, US, pages 196-201 is directed to a CCD handheld camera having a single matrix circuit. This document discusses the influence of the matrix ratio on the alias signal. OBJECT AND SUMMARY OF THE INVENTION The purpose of the present invention is to offer a video camera in which the effect of the chromatic aberration is suppressed sufficiently, even at such parts close to the periphery of the imaging plane, and that, even for those colors not containing green light the moire suppression capability by the offset sampling scheme is attainable. Another purpose of the present invention is, by using a simple circuit configuration, to suppress the moire completely for colors which contain red light and blue light at the same level. Further purpose of the present invention is to suppress the moire completely for colors which contains red light and blue light at the same level, and also to exclude the luminance error. Still another purpose of the present invention is to suppress the moire completely for all colors except for those pure colors of red and blue, and at the same time, to exclude the luminance error. In order to accomplish the above-mentioned purposes, a video camera of the present invention comprises an imaging part and a signal processing part having the following features. An imaging part comprises a prism for dividing an incident light L into four channels in total of two green channel lights, a blue channel light, and a red channel light, and four solid state imaging devices placed respectively for those four channel positions. Those two green channel solid state imaging devices are disposed offset mutually by a half pixel pitch in horizontal direction of frame. Those blue channel solid state imaging device and red channel solid state imaging device are also placed by offsetting them mutually by a half pixel pitch in the horizontal direction. From these four solid state imaging devices, video signals corresponding to their respective color channels are outputted. The signal processing part is comprised of a white balance circuit, at least one matrix circuit and a mixing circuit. The white balance circuit performs operations of addition of two green channel signals as well as performing the white balancing operation among those red, green, and blue channel signals out of those video signals outputted from the imaging part. The matrix circuit produces a luminance signal by combining those green, blue and red channel signals outputted from the white balance circuit with a specified matrix ratio. In a first matrix circuit its matrix ratio is set to a ratio determined by a television standard being in use. In a second matrix circuit its matrix ratio is set different from a ratio determined by a television standard and is changed adaptively in a control loop according to the amplitude of the high frequency component of respective ones of the color channel signals. The mixing circuit makes an addition of outputs of the first and the second matrix circuits and issues it. In such configuration, since two green channel solid state imaging devices are mutually pixel-offset in the horizontal direction in the imaging part, the moire effect can be suppressed without receiving the effect of the lens chromatic aberration even at the peripheral part of the imaging plane. Since the red channel solid state imaging device and the blue channel solid state imaging device are also pixel-offset, the moire suppression effect owing to the pixel offset is achieved also for those colors not containing green light. It is preferable to set the matrix ratio of the second matrix circuit in the signal processing part to a ratio at which a higher moire suppression effect can be obtained. And, a final luminance signal should be outputted by adding low frequency components of the first matrix circuit output and high frequency components of the second matrix circuit output. By the above-mentioned configuration, the luminance error can be suppressed by combining the low frequency signal of the luminance signal in accordance with the matrix ratio prescribed by a television standard in use; and by taking the high frequency signal of a matrix ratio suitable for getting a higher moire suppression effect, it becomes possible to make the moire suppression effect optimum. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a block diagram of a video camera concerning a first embodiment of the present invention. FIG.2 is a structural drawing showing the relation between lens 4 and imaging part 1 concerning the first embodiment of the present invention. FIG.3 is a conceptual drawing showing the positional relation between an optical image and two solid state imaging devices in case of applying the horizontal pixel offset in the first embodiment of the present invention. FIG.4 is a conceptual drawing showing the optical positional relation between pixels of four solid state imaging devices in the first embodiment and a waveform obtained from an optical image focused thereon. FIG.5 is a block diagram of a signal processing circuit of a video camera of the first embodiment of the present invention. FIG.6 is a block diagram of a signal processing of a video camera of the second embodiment of the present invention. FIG.7 is a block diagram of a second matrix circuit of the third embodiment of the present invention. FIG.8 is a block diagram of a second matrix circuit of the fourth embodiment of the present invention. FIG.9 is a block diagram of a second matrix circuit of the fifth embodiment of the present invention. FIG.10 is a graph of a frequency characteristic showing moire occurring as a function of frequency. DESCRIPTION OF THE PREFERRED EMBODIMENTS FIRST EMBODIMENT In FIG.1 which is a block diagram of a video camera concerning a first embodiment of the present invention, the configuration comprises an imaging part 1, a driving part 2, a signal processing part 3, and a lens 4. An optical image incident through the lens 4 is focused on a solid state imaging device which is a composing element of the imaging part 1. The driving part 2 generates driving pulses for driving the solid state imaging devices and drives the solid state imaging devices. The signal processing part 3 performs its processing on the video signals issued from the solid state imaging devices and issues output signals. FIG.2 is a structural drawing showing the relation between lens 4 and imaging part 1 concerning the first embodiment of the present invention. The imaging part 1 comprises a prism 201, which is for decomposing an incident optical image into four images of different color channels, and a set of four solid state imaging devices 202, 203, 204, 205 provides for those four color channels. The set of four solid state imaging devices consists of a solid state imaging device 202 for red channel, a solid state imaging device 203 for blue channel, a solid state imaging device 204 for a first green channel and a solid state imaging device 205 for a second green channel. For an optical image incident through a lens 4, first, a blue light component is reflected by a reflecting plane 206 and focused on the blue channel solid state imaging device 203. Among those light components transmitting through the first reflecting plane 206, a red light component is further reflected by a second reflecting plane 207 and is focused on the red channel solid state imaging device 202. Still further, a green channel light which has been transmitted through a reflecting plane 208 is divided into two by a half mirror 209, and they are respectively focused on the first green channel solid state imaging device 204 and the second green channel solid state imaging device 205. Those solid state imaging devices 202, 203, 204, and 205 sample the optical images focused thereon, perform the optoelectric conversion and issue respective video signals corresponding to their respective optical images. FIG.3 is a conceptual drawing showing the optical relation between an optical image and two solid state imaging devices in case of applying the horizontal pixel offset in the first embodiment of the present invention. Pixels on a first solid state imaging device 301 are shown by small open (white) circles as shown in (a), whereas pixels on a second solid state imaging device 302 are shown by small filled (black) circles as shown in (b). They are arranged in such a way that they are offset mutually by a half of pixel pitch in the horizontal direction with respect to the optical image as shown in (c). Positional relation between these two solid state imaging devices 301 and 302 corresponds to that between the first green channel solid state imaging device 204 and the second green channel solid state imaging device 205 or that between the red channel solid state imaging device 202 and the blue channel solid state imaging device 203. Accordingly, by utilizing the outputs of those two solid state imaging devices, signal having a band width as broad as twice of that of the conventional imaging device having a single solid state imaging device can be obtained. FIG.4 is a conceptual drawing showing the optical positional relation between pixels of four solid state imaging devices in the first embodiment and a waveform obtained from an optical image focused thereon. In FIG.4, a waveform 401 shows an intensity distribution on a horizontal scanning line of an optical image determined by an object, wherein sample points are represented by small open circles. And, relative sampling positions on a horizontal scanning line determined by pixels respectively of the red channel solid state imaging device 202, the blue channel solid state imaging device 203, the first green channel solid state imaging device 204, and the second green channel solid state imaging device 205 are shown in a lower part of FIG.4. In a first embodiment, the first and the second green channel solid state imaging devices 204 and 205 are mutually pixel-offset, and furthermore, the red channel solid state imaging device 202 and the blue channel solid state imaging device 203 are arranged with a pixel offset. And the red channel solid state imaging device 202 and the first green channel solid state imaging device 204 are placed at such positions where they receive the same optical image; while the blue channel solid state imaging device 203 and the second green channel solid state imaging device 205 are placed at positions where they receive the same optical image. As is known from this, the object image is sampled by a doubled sampling frequency by the use of two green channel solid state imaging devices, and also by use of the red channel solid state imaging device and the blue channel solid state imaging device, a sampling at a doubled sampling frequency is performed. FIG.5 is a circuit block diagram of the signal processing circuit 3 of the video camera in accordance with the first embodiment of the present invention. As shown in FIG.5, the signal processing part 3 comprises a first delay line 501 for delaying a second green channel signal, a second delay line 502 for delaying a blue channel signal, a white balance circuit 503 which receives output signals from the first delay line 501, the second delay line 502, the output signal of the first green channel solid state imaging device 204 and the output signal of the red channel solid state imaging device 202, and a matrix circuit 504, which receives output signals Vr, Vg and Vb for red channel, green channel and blue channel, respectively, from the white balance circuit 503. That is, the video signals issued from the first green channel solid state imaging device 204 and the red channel solid state imaging device 202 are inputted directly to a white balance circuit 503. The video signals issued from the second green channel solid state imaging device 205 and the blue channel solid state imaging device 203 are delayed by a half of the pixel period by the first delay line 501 and the second delay line 502, respectively, and inputted into the white balance circuit 503. In the white balance circuit 503, firstly the first and the second green channel signals are added to each other at a ratio of 1 : 1. Then by adding signals from mutually pixel-offset solid state imaging devices, a composite wide band green channel signal is produced. Thus, the output signals of the first and the second green channel solid state imaging devices are combined into one. Thus, by doubling the number of pixel for green light for which human eyes have a high sensitivity, the image signal is made to have a wide frequency range. Next, the white balance is taken by controlling the gains of the red channel signal, the blue channel signal and the green channel signal so as to make the levels of these three signals equal with each other at a time when the reference white is imaged. The white-balanced respective color channel signals are inputted into a matrix circuit 504. In the matrix circuit, respective color signals are combined by a matrix ratio determined by a television standard being in use, and thereby the luminance signal is determined to be Vy. When the matrix ratio among the red channel signal Vr, the green channel signal Vg, and the blue channel signal Vb are set to be Kr : Kg : Kb, the luminance signal Vy is combined in accordance with a relation: Vy = Kr×Vr + Kg×Vg + Kb×Vb , where Kr, Kg, and Kb are constants fulfilling a relation of Kr + Kg + Kb = 1 . At this time, the matrix ratios are set as follows: (i) in the Hi-Vision system, Kr = 0.2125, Kg = 0.7154, Kb = 0.0721 , (ii) in the NTSC television system, Kr = 0.299, Kg = 0.587, Kb = 0.114 . Here, explanation is given on the moire suppression effect by the offset sampling. FIG.10 is a graph of a frequency characteristic showing moire occurring as a function of frequency. The moire takes place due to the fact that the optical image is sampled by pixels. It is an aliasing noise occurring in a frequency range around a half of sampling frequency, the Nyquist frequency, having it as its center frequency. As is shown in FIG.10, with respect to a moire component contained in the output from the one of those two solid state imaging devices which are mutually offset by a half pixel pitch, a moire component contained in the output from the other solid state imaging devices is offset by an amount of phase of 180° . Therefore, by adding them to each other, the moires contained in those two outputs are canceled, thereby the suppression of moire becomes possible. At time when two signals are added to each other, if the signal levels of those two outputs are equal, the levels of the moire component are also equal, and hence it becomes possible to suppress the moire perfectly. According to the first embodiment of the present invention, the following effects are obtained. By introducing the pixel offset between the first and the second green solid state imaging devices, even the peripheral part of the imaging plane does not suffer from the effect of lens chromatic aberration, hence the moire suppression effect is not impeded. Furthermore, since the blue channel and the red channel solid state imaging devices are also mutually offset, in the luminance signal which is obtained by combining respective color signals the moire suppression effect can be obtained even for an object including only blue light and red light but excluding green light. In addition, as a result of pixel offsetting between the first and second green solid state imaging color devices, also for all colors, e.g., colors other than pure red color and pure blue color, for example, for color of green or for colors including both blue and red color the moire suppression effect can be obtained. SECOND EMBODIMENT Explanation is given on a video camera in accordance with a second embodiment of the present invention. The configuration of the second embodiment is the same as that of the first embodiment for the imaging part 1, the driving part 2, and for the lens 4, whereas the configuration of the signal processing part is different. In the following, the configuration and the action of the signal processing part is explained. FIG.6 is a circuit block diagram of a signal processing circuit 3 of the video camera in accordance with the second embodiment of the present invention. The signal processing part 3 comprises a first delay line 601 for delaying a second green channel signal, a second delay line 602 for delaying a blue channel signal, a white balance circuit 603, a first matrix circuit 604 and a second matrix circuit 605 both of which receive output signals of the white balance circuit 603, a high-pass filter 607 and a low-pass filter 608 which receive output signals Vy2 and Vy1 of the second matrix circuit 605 and the first matrix circuit 604, respectively, and a mixing circuit 609 which receives output signals of the high-pass filter 607 and the low-pass filter 608. The actions of signals from issuance from the solid state imaging devices 202, 203, 204, and 205 corresponding to respective color channels in FIG.2 to passing through the white balance circuit 603 are the same as those of the first embodiment. The respective color channel signals Vr, Vg and Vb outputted from the white balance circuit 603 are respectively separated into two routes and inputted into the first matrix circuit 604 and the second matrix circuit 605. The first matrix circuit 604 works the same action as the matrix circuit 504 in the first embodiment, and outputs a first luminance signal Vy1. Defining the matrix ratio as Kr:Kg:Kb for the red channel signal Vr, the green channel signal Vg, and the blue channel signal Vb, the second matrix circuit 605 produces the second luminance signal output Vy2 which fulfills the following equation: Vy2 = Kr × Vr + Kg × Vg + Kb × Vb , where the constants Kr, Kg, and Kb fulfill the following relation: Kr + Kg + Kb = 1 . The matrix factor Kg for the green channel signal is set to a matrix factor determined by a television standard being in use; the matrix factors Kr and Kb respectively for the red channel signal and the blue channel signal are set to the same factor determined by(1-Kg)/2 Therefore, the matrix ratio of the second matrix circuit is set as follows: (i) in the High-Vision system, Kr = 0.1423, Kg = 0.7154, Kb = 0.1423, and (ii) in the NTSC television system, Kr = 0.2065, Kg = 0.587, Kb = 0.2065 . Next, the first luminance signal Vy1 having passed through a low pass filter 608 and a second luminance signal Vy2 having passed through a high-pass filter 607 are inputted into a mixing circuit 609. In the mixing circuit, these two signals are added to each other and outputted finally as the luminance signal Vy of a video camera. According to the second embodiment of the present invention, the following technical advantage is obtained. In the low frequency range of the luminance signal, the matrix ratio is set to a ratio determined by a television standard being in use, and hence the luminance error does not take place. In the high frequency range of the luminance signal, after setting the matrix factor of the green channel signal, which has a relatively large factor within the luminance signal, to a factor determined by a television standard being in use, then those factors for the red channel signal and blue channel signal are calculated. Therefore, occurrence of the luminance error can be made small. Furthermore, by combining the red channel signal and the blue channel signal in the same ratio, the signal levels of the red channel and the blue channel become equal at the time of signal addition in the mixing circuit. Therefore, it becomes possible to suppress completely the occurrence of moire for those colors containing red light component and blue light component at the same level as the color of e.g. pure white. THIRD EMBODIMENT Explanation is given on a video camera in accordance with a third embodiment with reference to FIG.7. In the present embodiment, its configuration and action is similar to those of the second embodiment shown in FIG.6. The only difference of the third embodiment from the second embodiment is the configuration and action of the second matrix circuit 605 of FIG.6 of the second embodiment. FIG.7 is a block diagram showing detailed configuration of a second matrix circuit of the third embodiment of the present invention. The matrix circuit comprises a green channel amplifier 701 for amplifying a green channel signal, a red channel multiplier 702 for multiplying a red channel signal, a blue channel multiplier 703 for multiplying a blue channel signal, a high frequency amplitude detection circuit 704 for the red channel signal, a high frequency amplitude detection circuit 705 for the blue channel signal, a factor deriving circuit 706 which receives outputs of the high frequency amplitude detection circuits 704 for the red channel signal and the high frequency amplitude detection circuits 705 for the blue channel signal thereby issue multiplying factor signal to the red channel multiplier 702 and to the blue channel multiplier 703, and an addition circuit 707 for summing outputs of the green channel amplifier 701, the red channel multiplier 702 and the blue channel multiplier 703 thereby to issue summed signal as the second luminance signal Vy2. In the following, explanation is given on a method of setting the factors in the second matrix circuit. The condition of the second matrix circuit 605 required in the third embodiment is to make the level of the produced second luminance signal Vy2 issued from the second matrix circuit 605 equal to the level of the first luminance signal Vy1 given from the first matrix circuit 604, when combining in a matrix ratio determined by the television standard even in the high frequency range so as to eliminate the luminance error. At the same time, this configuration must suppress the moire completely for those colors in which the red light component and the blue light component are contained at the equal level, that is, for colors such as white, magenta, and green. In order to achieve the above-mentioned condition, the matrix factors Kr and Kb of the red channel signal and of the blue channel signal are adjusted adaptively responding to the red and blue high frequency amplitudes. In the following, method of calculation of factors is explained. Taking the matrix ratio determined by the television standard having red, green, and blue channel signals Vr, Vg, and Vb to be kr:kg:kb (where kr + kg + kb = 1), the first luminance level Vy1 is expressed as: Vy1 = kr×Vr + kg×Vg + kb×Vb . And taking the matrix ratio to be sought as Kr:Kg:Kb, the second luminance level Vy2 to be outputted is expressed as: Vy2 = Kr×Vr + Kg×Vg + Kb×Vb . As for the condition for eliminating the luminance error, it is necessary to fulfill a condition Vy2 = Vy1 . The above-mentioned equation means that the level of Vy2 produced by setting a matrix ratio, which is different from a matrix ratio determined by the television standard, becomes equal to the level of Vy1 produced at a matrix ratio determined by the television standard. Furthermore, concerning those colors in which the red light component and the blue light component are contained at the equal level such as pure white, for suppressing the moire completely, it is necessary to make the signal levels of the red channel and the blue channel equal by setting as: Kr = Kb . Then, letting high frequency amplitude voltages of the red and the blue channel signals to be Ar and Ab, and taking the matrix factor Kg of the green channel signal to be kg which is determined from the television standard, from the conditional equations (11) and (12), the following relation holds; Kr×Ar + Kb×Ab = kr×Ar + kb×Ab . By solving this equation about Kb, the following relation is obtained; Kb = ( kr×Ar + kb×Ab ) / ( Ar + Ab ) . Accordingly, the matrix factors of respective color signals in the second matrix circuit are set as follows; Kr = Kb = ( kr×Ar + kb×Ab ) / ( Ar + Ab ) , Kg = kg . Explanation is given on the action of the matrix circuit for realizing these ratios. Among those respective color channel signals inputted to the matrix circuit, the red channel signal Vr is inputted to the red channel multiplier 702 and the red channel high frequency signal amplitude detection circuit 704. Similarly a blue channel signal is inputted to the blue channel multiplier 703 and the blue channel high frequency amplitude detection circuit 705. The multipliers 702 and 703 have two input terminals and each outputs a signal proportional to a multiplication of these two input signals. The red channel high frequency amplitude detection circuit 704 detects the signal amplitude in the high frequency range of the red channel signal and outputs the red signal high frequency amplitude voltage Ar to the factor deriving circuit 706. The blue channel high frequency amplitude detection circuit 705 also detects the signal amplitude in the high frequency range of the blue channel signal and outputs the blue signal high frequency amplitude voltage Ab to the factor deriving circuit 706. The factor deriving circuit 706 computes or produces the matrix factors Kr and Kb which were derived before, and input them respectively to the red channel multiplier 702 and the blue channel multiplier 703. The red channel multiplier 702 and the blue channel multiplier 703 perform their multiplication function on the red and blue channel signals Vr and Vb by multiplying them by their respective matrix factors Kr and Kb and output them. Among those respective color channel signals inputted to the matrix circuit, the green channel signal Vg is inputted to the green channel amplifier 701 and its amplification gain is set to be Kg as matrix factor for green channel. Thus, those respective color channel signals which were already multiplied by matrix factors are inputted to the addition circuit 707 and outputted as a second luminance signal Vy2. Therefore, in accordance with the third embodiment of the present invention, the following effects are obtained. In the low frequency range of the luminance signal, since the matrix ratio is taken to be a ratio determined by a television standard being in use, the luminance error does not occur. In the high frequency range of the luminance signal, the matrix factor of the green channel, which has a large occupying factor within the luminance signal is set as a factor determined by a television standard being in use, and those factors for the red channel signal and blue channel signal are set to such factors that which are mutually equal so that the second luminance signal level becomes equal to the first luminance signal level determined by the television standard being in use. By the above-mentioned settings of the matrix factors, the luminance error can be eliminated. By combining the red signal and blue signal with the same ratio, the moire is completely suppressed with regard to those colors containing the red light component and the blue light component at the equal level such as pure white, magenta or green. FOURTH EMBODIMENT Explanation is given on a video camera in accordance with the fourth embodiment of the present invention. In this fourth embodiment, the configuration and action are similar to the configuration and action of the second embodiment of FIG.6. The only difference of the fourth embodiment from the second embodiment is configuration and action of the second matrix circuit 605 of Fig.6 in the second embodiment. FIG.8 is a block diagram of a second matrix circuit by the fourth embodiment of the present invention. The matrix circuit comprises a green channel amplifier 801, a red channel multiplier 802, a blue channel multiplier 803, a red channel high frequency amplitude detection circuit 804, a blue channel high frequency amplitude detection circuit 805, a red channel factor deriving circuit 806 which receives outputs from the red channel high frequency amplitude detection circuit 804 and the blue channel high frequency amplitude detection circuit 805 and issues a red channel factor signal Kr to the red channel multiplier 802, a blue channel factor deriving circuit 807 which receives outputs from the blue channel high frequency amplitude detection circuit 805 and the red channel high frequency amplitude detection circuit 804 and issues a blue channel factor signal Kb to the blue channel multiplier 803, and an addition circuit 808 for summing outputs of the green channel amplifier 801, the red channel multiplier 802 and the blue channel multiplier 803 thereby to issue summed signal Vy2 as the second luminance signal Vy2. In the following, explanation is given on a method of setting the factors Kr and Kb in the second matrix circuit 605. The condition of the second matrix circuit 605 required in the fourth embodiment is to make the level of the produced second luminance signal Vy2 issued from the second matrix circuit 605 equal to the level of the normal luminance signal determined by the television standard even in the high frequency range, that is, to eliminate the luminance error. And, also to suppress the moire completely for colors other than pure colors of red and blue. Then matrix factors Kr and Kb of the red channel signal and of the blue channel signal are changed adaptively responding to the red and blue high frequency amplitudes. In the following, method of calculation of factors is explained. Taking the matrix ratio determined by the television standard having red, green, and blue channel signals Vr, Vg, and Vb to be kr:kg:kb (where kr + kg + kb = 1), the first luminance level Vy1 is expressed as: Vy1 = kr×Vr + kg×Vg + kb×Vb . And taking the matrix ratio to be sought as Kr:Kg:Kb, the second luminance level Vy2 to be outputted is expressed as: Vy2 = Kr×Vr + Kg×Vg + Kb×Vb . As the condition for eliminating the luminance error, it is necessary to fulfill a condition Vy2 = Vy1 . The above-mentioned equation means that the level of Vy2 produced by setting a matrix ratio, which is different from a matrix ratio determined by the television standard, becomes equal to the level of Vy1 produced at a matrix ratio determined by the television standard. Furthermore for those colors in which the red light component and the blue light component are contained at the equal level, to suppress the moire completely, it is necessary to make the signal levels of the red channel and the blue channel equal by setting as Kr×Vr = Kb×Vb . Then, letting high frequency amplitude voltages of the red and the blue channel signals to be Ar and Ab, and taking the matrix factor Kg of the green channel signal to be kg which is determined from the television standard, from the conditional equations (17) and (18), the following relation holds: 2×Kr×Ar = kr×Ar + kb×Ab . 2×Kb×Ab = kr×Ar + kb×Ab . By solving these equations about Kb, the following relation is obtained; Kr = ( kr×Ar + kb×Ab ) / ( 2×Ar ) , Kb = ( kr×Ar + kb×Ab ) / ( 2×Ab ) . Accordingly, the matrix factors of respective color signals in the second matrix circuit are set as follows; Kr = ( kr×Ar + kb×Ab ) / ( 2×Ar ) , Kg = kg , Kb = ( kr×Ar + kb×Ab ) / ( 2×Ab ) . Explanation is given on the action of the matrix circuit for realizing these ratios. Among those respective color channel signals inputted to the matrix circuit, the red channel signal Vr is inputted to the red channel multiplier 802 and the red channel high frequency amplitude detection circuit 804. Similarly a blue channel signal is inputted to the blue channel multiplier 803 and the blue channel high frequency amplitude detection circuit 805. The multipliers 802 and 803 have two input terminals and each outputs a signal proportional to a multiplication between these two input signals. The red channel high frequency amplitude detection circuit 804 detects the signal amplitude in the high frequency range of the red channel signal and outputs a red signal high frequency amplitude voltage Ar to the red channel factor deriving circuit 806 and the blue channel factor deriving circuit 807. The blue channel high frequency amplitude detection circuit 805 also detects the signal amplitude in the high frequency range of the blue channel signal and outputs a blue signal high frequency amplitude voltage Ab to the red channel factor deriving circuit 806 and the blue channel factor deriving circuit 807. The red channel factor deriving circuit 806 computes or produces the matrix factors Kr which was derived before, and outputs it to the red channel multiplier 802. The blue channel factor deriving circuit 807 computes or produces the matrix factor Kb which was derived before, and outputs it to the blue channel multiplier 803. The red and the blue channel multipliers 802 and 803 perform their multiplication function on the red and blue channel signals Vr and Vb by multiplying them by their respective matrix factors Kr and Kb and output them to the addition circuit 808. Among those respective color channel signals Vg, Vr and Vb inputted to the matrix circuit 605, the green channel signal Vg is inputted to the green channel amplifier 801 and its amplification gain is set to be Kg as a matrix factor for green channel. Thus those respective color channel signals which were already multiplied by matrix factors are inputted to the addition circuit 808 and outputted as a summed second luminance signal Vy2. Therefore, according to the fourth embodiment of the present invention, the following technical effects are obtained. In the low frequency range of the luminance signal, the matrix ratio is taken to be a ratio determined by a television standard in use, and therefore the luminance error does not occur. In the high frequency range of the luminance signal, the matrix factors are set as follows: (i) the matrix factor of the green channel, which has a large occupying factor within the luminance signal, is set to a factor determined by a television standard in use, and on the other hand, (ii) the matrix factors for the red channel signal and blue channel signal are set so that the second luminance signal level becomes equal to the first luminance signal level, which has been combined with factors determined by the television standard in use. By the above-mentioned settings of the matrix factors, the luminance error can be eliminated. By combining the red signal and blue signal in the same level, the moire is suppressed completely for colors other than the pure colors of red and blue. FIFTH EMBODIMENT Explanation is given on a fifth embodiment of video camera in accordance with the fifth embodiment of the present invention with reference to FIG.9. In the present embodiment, its configuration and action are almost the same to that of the second embodiment, but the configuration and action of the second matrix circuit 605 in FIG.6 which has been used for the second embodiment is different. In the following, explanation is given on the second matrix circuit 605 shown in FIG.9. FIG.9 is a block diagram of a second matrix circuit 605 of the fifth embodiment of the present invention. The matrix circuit 605 comprises a green channel amplifier 901, a red channel multiplier 902, a blue channel multiplier 903, a red channel high frequency amplitude detection circuit 904, a blue channel high frequency amplitude detection circuit 905, a red channel factor deriving circuit 906 which receives outputs of the red channel high frequency amplitude detection circuit 904 and the blue channel high frequency amplitude detection circuit 905 and issues a red channel factor signal Kr to the red channel multiplier 902 and further a blue channel factor signal Kb to the blue channel multiplier 903, and an addition circuit 907 for summing outputs of the green channel amplifier 901, the red channel multiplier 902 and the blue channel multiplier 903 thereby to issue summed signal Vy2 as the second luminance signal Vy2. Among respective color channel signals inputted into the matrix circuit, the red channel signal Vr is inputted into the red channel multiplier 902 and the red channel high frequency amplitude detection circuit 904. Similarly, the blue channel signal is inputted into the blue channel multiplier 903 and the blue channel high frequency amplitude detection circuit 905. These multipliers 902, 903 respectively have two inputs, namely red channel signal Vr and blue channel signal Vb from the white balance circuit 603 and the red channel factor signal Kr and the blue channel factor signal Kb from the factor deriving circuit 906. And the multipliers 902 and 903 respectively output signals of multiplication of those two kinds of inputs. The action of the second matrix circuit 605 of FIG.9 is as follows. The red channel high frequency amplitude detection circuit 904 detects the amplitude of high frequency range of the red channel signal Vr and gives the red channel high frequency voltage Ar to the channel factor deriving circuit 906. The blue channel high frequency amplitude detection circuit 904 detects the amplitude of high frequency range of the blue channel signal Vb and gives the blue channel high frequency voltage Ab to the channel factor deriving circuit 906. The channel factor deriving circuit 906 computes and produces the red channel matrix factor Kr and the blue channel matrix factor Kb gives them respectively to the red and the blue channel multipliers 902 and 903. The red and the blue channel multipliers 902 and 903 respectively multiply the red and the blue channel signals Vr and Vb by respective matrix factors Kr and Kb and outputs the products to the addition circuit 907. Among respective color channel signals inputted into the matrix circuit 605, the green channel signal Vg is inputted into the green channel multiplier 901 whereof the amplification gain is Kg as matrix factor for green channel. The red channel signal Vr is inputted into the red channel multiplier 902, whereof the matrix factor is Kr. The blue channel signal Vb is inputted into the blue channel multiplier whereof the matrix factor is Kb. In this manner, those respective color channel signals multiplied by the respective matrix factors are inputted into the addition circuit 907 and outputted as a second luminance signal Vy2. Therefore, according to the fifth embodiment of the present invention, similar technical effects as the fourth embodiment are obtained.

Claims: A solid state video camera comprising: an imaging part (1) having a prism (201) for decomposing incident light into four color channels and four solid state imaging devices (202, 203, 204, 205) placed at respective light output parts of respective color channels, for outputting video signals corresponding to said respective color channels, characterized by a signal processing part (3) having a white balance circuit (603) and first and second matrix circuits (604, 605) wherein video signals corresponding to respective color channels outputted from those four solid state imaging devices are processed in the white balance circuit and thereafter inputted into said matrix circuits for being combined as luminance output signals Vy1 and Vy2, the matrix ratio of said second matrix circuit being changed adaptively in a control loop according to the amplitude of the high frequency component of respective ones of said color channel signals, so that an optimum moire suppression effect is obtainable. A solid state video camera in accordance with claim 1 wherein: said prism (201) has light output faces for issuing two green channel optical outputs, one blue channel optical output, and one red channel optical output, the two green channel solid state imaging devices (204 and 205) disposed respectively at said green channel optical outputs of said prism (201) are arranged in a manner that they are offset mutually by a half of pixel pitch in the horizontal direction with respect to the optical image, and the red channel solid state imaging device (202) disposed at said red channel optical output of said prism and the blue channel solid state imaging device (203) placed at said blue channel optical output of said prism are offset mutually by a half of pixel pitch in the horizontal direction. A solid state video camera in accordance with claim 2 wherein in said signal processing part (3): said white balance circuit (603) carries out white balance adjustment after summing up the outputs of the first and the second green channel solid state imaging devices (204, 205) of the imaging part (1) in a ratio 1 : 1, in said first matrix circuit (604), the matrix ratio is set to a ratio determined by a television standard in use, a mixing circuit (609) makes a sum of said outputs Vy1 and Vy2 of said first matrix circuit (604) and said second matrix circuit (605) and issues a luminance output signal Vy. A solid state video camera in accordance with claim 3 wherein in said second matrix circuit: provided that the matrix ratio of said first matrix circuit (604) determined by the television standard is kr:kg:kb, where kr+kg+kb=1, and that a high frequency component amplitude of the red channel signal Vr is Ar, and a high frequency component amplitude of the blue channel signal Vb is Ab, the matrix ratio Kr:Kg:Kb of said second matrix circuit (605) is set as: Kr = (kr x Ar + kb x Ab )/( Ar + Ab ), Kg = kg, Kb = (kr x Ar + kb x Ab ) / ( Ar + Ab ). A solid state video camera in accordance with claim 4, wherein said second matrix circuit (605) comprises a green channel amplifier (701), a red channel multiplier (702), a blue channel multiplier (703), a red channel high frequency amplitude detection circuit (704), a blue channel high frequency amplitude detection circuit (705), a factor deriving circuit (706), and an addition circuit (707), said red channel signal is inputted into said red channel multiplier (702) and to said red channel high frequency amplitude detection circuit (704), said blue channel signal is inputted into said blue channel multiplier (703) and to said blue channel high frequency amplitude detection circuit (705), said factor deriving circuit (706) has two inputs for receiving two amplitude detection voltages from said red high frequency amplitude detection circuit (704) and said blue channel high frequency amplitude detection circuit (705) and computes matrix factors thereby and outputs them respectively to said red channel multiplier (702) and said blue channel multiplier (703), thereby to control said red channel multiplier (702) and said blue channel multiplier (703) in a manner to have necessary multiplication factors for inputted red channel signal and blue channel signal, said green channel amplifier (701) has an amplification gain Kg, thereafter said red, blue, and green channel signals are summed up to each other in said addition circuit (707) and outputted as the second luminance signal Vy2. A solid state video camera in accordance with claim 3 wherein in said second matrix circuit: provided that the matrix ratio of said first matrix circuit (604) determined by the television standard is kr:kg:kb , where kr+kg+kb=1, and that a high frequency component amplitude of the red channel signal Vr is Ar, and a high frequency component amplitude of the blue channel signal Vb is Ab, the matrix ratio Kr:Kg:Kb of said second matrix circuit (605) is set as: Kr = (kr x Ar + kb x Ab ) / ( 2 xAr ), Kg = kg, Kb = (kr x Ar + kb x Ab ) / ( 2 x Ab ). A solid state video camera in accordance with claim 6 wherein said second matrix circuit (605) comprises a green channel amplifier (801), a red channel multiplier (802), a blue channel multiplier (803), a red channel high frequency amplitude detection circuit (804), a blue channel high frequency amplitude detection circuit (805), a red channel factor deriving circuit (806), a blue channel factor deriving circuit (807), and an addition circuit (808), said red channel signal is inputted into said red channel multiplier (802) and to said red channel high frequency amplitude detection circuit (804), said blue channel signal is inputted into said blue channel multiplier (803) and to said blue channel high frequency amplitude detection circuit (805), said red channel factor deriving circuit (806) has two inputs for receiving two amplitude detection voltages from said red channel high frequency amplitude detection circuit (804) and said blue channel high frequency amplitude detection circuit (805) and computes matrix factor thereby and outputs it to said red channel multiplier (802), thereby to control said red channel multiplier (802) in a manner to make necessary multiplication factor corresponding to inputted red channel signal, said blue channel factor deriving circuit (807) has two inputs for receiving two amplitude detection voltages from said red channel high frequency amplitude detection circuit (804) and said blue channel high frequency amplitude detection circuit (805) and computes matrix factor thereby and outputs it to said blue channel multiplier (803), thereby to control said blue channel multiplier (803) in a manner to make necessary multiplication factor corresponding to inputted blue channel signal, said red channel multiplier (802) and said blue channel multiplier (803) perform respectively their functions of multiplying respective inputted red and blue channel signals by their respective matrix factors and output them, said green channel amplifier (801) has an amplification gain Kg, thereafter said red, blue, and green channel signals are summed up to each other in said addition circuit (808) and outputted as the second luminance signal, Vy2. A solid state video camera in accordance with claim 6 wherein said second matrix circuit (605) comprises a green channel amplifier (901), a red channel multiplier (902), a blue channel multiplier (903), a red channel high frequency amplitude detection circuit (904), a blue channel high frequency amplitude detection circuit (905), a factor deriving circuit (906), and an addition circuit (907), said red channel signal is inputted into said red channel multiplier (902) and to said red channel high frequency amplitude detection circuit (904), said blue channel signal is inputted into said blue channel multiplier (903) and to said blue channel high frequency amplitude detection circuit (905) said factor deriving circuit (906) has two inputs for receiving two amplitude detection voltages from said red channel high frequency amplitude detection circuit (904) and said blue channel high frequency amplitude detection circuit (905) and computes matrix factors thereby and outputs a factor signal to said red channel and the blue channel multipliers (902, 903) thereby to control said red and blue channel multipliers (902, 903) in a manner to make necessary multiplication factor corresponding to inputted red and blue channel signals, said red channel multiplier (902) and said blue channel multiplier (903) perform respectively their functions of multiplying respective inputted red and blue channel signals by their respective matrix factors and output them, said green channel amplifier (901) has an amplification gain Kg, thereafter said red, blue, and green channel signals are summed up to each other in said addition circuit (907) and outputted as the second luminance signal Vy2.

Inventors: FUJITA YOSHIHIRO, KANNO HIROSHI, MITANI KOHJI, NINOMIYA YUICHI, SAITOH TOSHINORI, SUETSUGI KEISUKE, SUGAWARA MASAYUKI, FUJITA, YOSHIHIRO, KANNO, HIROSHI, MITANI, KOHJI, NINOMIYA, YUICHI, SAITOH, TOSHINORI, SUETSUGI, KEISUKE, SUGAWARA, MASAYUKI
Applicants: JAPAN BROADCASTING CORP, MATSUSHITA COMMUNICATION IND, MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA COMMUNICATION INDUSTRIAL CO., LTD., MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD., NIPPON HOSO KYOKAI
Application year: 1994
Main classification: H04N9
IPC codes: H04N9